Adults have 4 air-filled sinuses on each side of the face. These are found in the cheekbones, forehead, and between the eyes. Inflammation in these sinuses can create swelling and excess mucus. This can block nasal breathing and drainage. The inflammation can have more than one cause. For example, you might have an infection. You might also have problems with your immune system or be sensitive to something you have breathed in. Chronic sinusitis can reduce your quality of life, ability to get restful sleep, and ability to work.